The aberration-corrected scanning transmission electron microscope (STEM) has emerged as a key tool for atomic resolution characterization of materials, allowing the use of imaging modes such as Z-contrast and spectroscopic mapping. The STEM has not been regarded as optimal for the phase-contrast imaging necessary for efficient imaging of light materials. Here, recent developments in fast electron detectors and data processing capability is shown to enable electron ptychography, to extend the capability of the STEM by allowing quantitative phase images to be formed simultaneously with incoherent signals. We demonstrate this capability as a practical tool for imaging complex structures containing light and heavy elements, and use it to solve the structure of a beam-sensitive carbon nanostructure. The contrast of the phase image contrast is maximized through the post-acquisition correction of lens aberrations. The compensation of defocus aberrations is also used for the measurement of three-dimensional sample information through post-acquisition optical sectioning.

The desire to study biology in situ has been aided by many imaging techniques. Among these, X-ray fluorescence (XRF) mapping permits observation of elemental distributions in a multichannel manner. However, XRF imaging is underused, in part, because of the difficulty in interpreting maps without an underlying cellular ‘blueprint'; this could be supplied using contrast agents. Carbon nanotubes (CNTs) can be filled with a wide range of inorganic materials, and thus can be used as ‘contrast agents' if biologically absent elements are encapsulated. Here we show that sealed single-walled CNTs filled with lead, barium and even krypton can be produced, and externally decorated with peptides to provide affinity for sub-cellular targets. The agents are able to highlight specific organelles in multiplexed XRF mapping, and are, in principle, a general and versatile tool for this, and other modes of biological imaging.

The extraordinary electrochemistry and the tunability of their energy levels allows the use of fulleropyrazolines in photovoltaics and charge-transfer systems. Here we show that substitution in position 1 tunes photolytic stability; electron-donating groups facilitate 1,3-dipolar cycloreversion to fullerene. This discovery has implications not only for photovoltaic stability but also highlights a potential strategy for photo-controlled fullerene release systems ('photo-caged'/'photo-activated' fullerene).

Historically, the scanning transmission electron microscope (STEM) has not been widely used for phase contrast imaging because the small bright‐field detector required makes use of only a small fraction of the incident electrons and is therefore inefficient with respect to dose. This limitation has hindered the efficient imaging of light elements in STEM. Alternative modes also have limitations. For example, annular dark‐field (ADF) imaging of graphene only makes use of a few percent of the incident electrons, and annular bright‐field imaging (ABF) requires lens aberrations to form an effective phase plate to get contrast from weakly scattering objects. Electron ptychography in the STEM was first demonstrated more than 20 years ago in the context of improving image resolution [1]. At that time, the image field of view was restricted by the limitations of the camera technology and data handling technology. Here we make use of the pnCCD (S)TEM camera, a direct electron pixelated detector from PNDetector, mounted on the JEOL ARM200‐CF aberration corrected microscope. The detector has a grid of 264x264 pixels and operates at a speed of 1000 frames‐per‐second (fps). The detector can achieve a speed of up to 20,000 fps through binning/windowing. ADF images can be recorded simultaneously, as shown by the schematic in Fig. 1. The resulting 4D data set is formed of a series of coherent convergent beam diffraction patterns recorded as a function of illuminating probe position. Here we explore how the bright‐field and dark‐field regions of scattering can be used to enhance the capabilities of STEM. We compare a range of methods that can be used to form the phase image from this data set, including single side‐band [2,3], Wigner distribution deconvolution [4] (used to produce Fig. 2) and ePIE [5]. Phase imaging using ptychography has a relatively simple transfer function [3] and also provides an inherent filter of image noise without reducing the signal strength to form high quality phase images (Fig. 2). Furthermore, the four‐dimensional data set is highly redundant and it is possible to detect and correct for residual aberrations in the image. The ability to deconvolve lens aberrations can further be used to extract three‐dimensional information from a single STEM image acquisition scan. This is achieved by reconstructing the phase image at a specific depth in the sample, which can be performed even though the microscope may not have been focused at that depth (Fig. 3). Finally, we explore the potential for using information outside the bright‐field disc to enhance STEM imaging.

Advances in fast pixelated detector technology have enabled coherent diffraction patterns in a scanning transmission electron microscope (STEM) to be recorded at every probe position to form a four dimensional (4D-) STEM dataset. The rich information contained in the 4D-STEM dataset has previously been poorly utilized by the STEM bright-field detector with a small collection angle, hindering the efficiency for imaging light elements. Furthermore, collecting the electron intensity using integrating detectors such as annular bright field and the annular dark field (ADF) detectors is not able to make full use of the diffraction information.Electron ptychography is a method for retrieving phase information using diffraction patterns acquired from a sequential array of overlapping illuminated areas, and has been first demonstrated on a 4D-STEM dataset more than 20 years ago for improving image resolution [1]. At that time, the image field of view was restricted by the limitations of the camera speed and computational processing power. Using a modern aberration-corrected STEM and a fast pixelated detector, quantitative phase images can be formed simultaneously with other STEM imaging modes such as ADF at atomic resolution [2]. This phase imaging mode has a monotonic phase contrast transfer function and provides an inherent filter of image noise without reducing the strength of the phase contrast [3].In this work we show that the large redundancy in phase information in the 4D-STEM data not only offers efficient phase imaging, but also allows lens aberrations to be detected and corrected through post-acquisition processing (Fig.1) by applying a ptychography method called Wigner-distribution deconvolution (WDD) [4]. The aberration measurement and correction method works on both amorphous and crystalline specimens. Moreover, three dimensional structure information is also available post-acquisition by reconstructing the phase image at a specific depth in the specimen along the e-beam direction, which can be performed even though the microscope may not have been focused at that depth (Fig.2). Theoretical calculations suggest that the three dimensional structure information using the WDD method is attributed to an optical sectioning effect, and our experimental results suggest that WDD optical sectioning gives a depth resolution that is equal to the depth of focus of the microscope.